The proposed research is a multi-faceted project aimed at elucidating the factors that affect both eukaryotic and prokaryotic gene expression in heterospecific environments. Its specific objectives are: 1) Isolation and characterization of promotor signals introduced into E. coli plasmids from selected prokaryotic and eukaryotic sources. 2) Investigation of the relationship between strength of promotor and level of expression of structural genes distal to the promotor. 3) Use of cloned and characterized promotors to express genes in an heterospecific environment. 4) Investigation of the structural and positional features of ribosomal binding sequences on heterospecific gene expression. 5) Study of effects of alterations in the primary sequence of the ribosomal binding site (rbs), the distance between the rbs and a distal translational start codon, and the secondary structure of the interposing sequence on translation of heterospecific mRNA. 6) Study of the role of intervening sequences (i.e., 'introns') of eukaryotic genomic DNA in the production of translational products encoded by this DNA vs. corresponding cDNA segments. 7) Investigation of the relationship between the location of introns and the structure of multi-component peptides that are expressed as a single precursor molecule. The proposed work is made possible by recently developed methods for the manipulation and cloning of DNA segments, and for the detailed analysis of DNA sequences at the nucleotide level.